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Chapter 18: Problem 33

What is a coupled reaction? What is its importance in biological reactions?

Short Answer

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A coupled reaction links exergonic and endergonic reactions, vital for energy transfer in biological processes.

Step by step solution

01

Understanding Coupled Reactions

A coupled reaction is when two chemical reactions are linked such that the energy released by one (exergonic reaction) drives the other (endergonic reaction). For example, the breakdown of ATP, which releases energy, is often used to power cellular processes that require energy.
02

Importance of Coupled Reactions in Biology

Coupled reactions are crucial in biological systems because they enable cells to carry out complex processes that require energy input. Without coupling, these processes would not be energetically feasible. It helps organisms efficiently use the chemical energy stored in molecules like ATP to drive functions such as muscle contraction, active transport, and biosynthesis.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Endergonic Reactions
Endergonic reactions are a type of chemical reaction where the energy of the products is greater than the energy of the reactants. In simpler terms, these reactions need an input of energy to proceed. They are often seen as non-spontaneous because they do not occur on their own without an external energy source.
Endergonic reactions are essential for various biological processes. For instance, they are involved in the synthesis of molecules in cells, such as the formation of proteins from amino acids.
  • Requires energy: Energy must be supplied for the reaction to happen.
  • Non-spontaneous: Does not occur naturally without energy input.
  • Example: Photosynthesis, where plants absorb sunlight to convert carbon dioxide and water into glucose and oxygen.
To facilitate these processes, cells often rely on exergonic reactions to provide the necessary energy.
Exergonic Reactions
Exergonic reactions are those in which the energy of the reactants is greater than the energy of the products, meaning there is a net release of energy. These reactions occur spontaneously because they result in a more stable energy state.
In biological systems, exergonic reactions are frequently used to release the energy stored in molecules, such as breaking down glucose during cellular respiration. This released energy can then be used to drive endergonic reactions through coupling.
  • Releases energy: Energy is released into the environment as the reaction proceeds.
  • Spontaneous: Likely to occur naturally as it results in a decrease in free energy.
  • Example: Cellular respiration, where glucose is broken down to release energy in the form of ATP to power cellular activities.
The energy output from exergonic reactions is often captured in the form of ATP, a molecule that stores energy for cellular use.
ATP (Adenosine Triphosphate)
ATP, or adenosine triphosphate, is the primary energy carrier in cells. It is often referred to as the "energy currency" of the cell. ATP stores energy in its high-energy phosphate bonds, which can be released when these bonds are broken.
The most common use of ATP in cells is through the coupling of reactions. Specifically, ATP hydrolysis, which is an exergonic process, provides energy to drive endergonic reactions.
  • Energy storage: Stores energy in chemical bonds, particularly between its phosphates.
  • High turnover rate: ATP is continuously regenerated as it is used up.
  • Key role in coupling: ATP hydrolysis releases energy that can be used to power endergonic reactions like muscle contractions and active transport in cells.
This ability to couple with both exergonic and endergonic reactions makes ATP indispensable in energy management and transfer in biological systems.

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Most popular questions from this chapter

Which of the following are not state functions: \(S, H,\) \(q, w, T ?\)

Ammonium nitrate \(\left(\mathrm{NH}_{4} \mathrm{NO}_{3}\right)\) dissolves spontaneously and endothermically in water. What can you deduce about the sign of \(\Delta S\) for the solution process?

Arrange the following substances ( 1 mole each) in order of increasing entropy at \(25^{\circ} \mathrm{C}\) : (a) \(\operatorname{Ne}(g)\) (b) \(\mathrm{SO}_{2}(g),(\mathrm{c}) \mathrm{Na}(s),(\mathrm{d}) \mathrm{NaCl}(s),(\mathrm{e}) \mathrm{H}_{2}(g) .\) Give the reasons for your arrangement.

How does the entropy of a system change for each of the following processes? (a) A solid melts. (b) A liquid freezes. (c) A liquid boils. (d) A vapor is converted to a solid. (e) A vapor condenses to a liquid. (f) A solid sublimes. (g) Urea dissolves in water.

Use the following data to determine the normal boiling point, in kelvins, of mercury. What assumptions must you make in order to do the calculation? $$ \begin{aligned} \mathrm{Hg}(l): & \Delta H_{\mathrm{f}}^{\circ} &=0 \text { (by definition) } \\\ & S^{\circ} &=77.4 \mathrm{~J} / \mathrm{K} \cdot \mathrm{mol} \\ \mathrm{Hg}(g): & \Delta H_{\mathrm{f}}^{\circ} &=60.78 \mathrm{~kJ} / \mathrm{mol} \\ & S^{\circ} &=174.7 \mathrm{~J} / \mathrm{K} \cdot \mathrm{mol} \end{aligned} $$
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